Variable power energy harvesting system

ABSTRACT

The disclosed invention provides examples of preferred embodiments including systems for harvesting energy from variable output energy harvesting apparatus. The systems include energy harvesting apparatus for providing energy input to a switched mode power supply and a control loop for dynamically adjusting energy harvesting apparatus input to the switched mode power supply, whereby system output power is substantially optimized to the practical. Exemplary embodiments of the invention include systems for harvesting energy using solar cells in boost, buck, and buck-boost configurations.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/982,893, filed Dec. 29, 2015, now U.S. Pat. No. 9,653,944, which is acontinuation of U.S. patent application Ser. No. 13/427,850, filed Mar.22, 2012, now U.S. Pat. No. 9,225,199, which claims priority to andbenefit of U.S. Provisional Patent Application Ser. No. 61/466,049,filed on Mar. 22, 2011, which is hereby incorporated by reference forall purposes as if set forth herein in its entirety.

TECHNICAL FIELD

The invention relates to electronic systems for the more efficientutilization of energy resources. More particularly, the inventionrelates to power control methods, systems, and microelectronic circuitrydesigned to facilitate the harvesting of useable power from variablepower energy sources such as, for example, photovoltaic systems.

BACKGROUND

Systems for harvesting energy from renewable resources have long beenpursued in the arts. One of the problems associated with engineeringenergy harvesting systems is the challenge of making maximum use ofenergy sources which may be intermittent in availability and/orintensity. Unlike traditional power plants, alternative energy sourcestend to have variable outputs. Solar power, for example, typicallyrelies on solar cells, or photovoltaic (PV) cells, used to powerelectronic systems by charging storage elements such as batteries orcapacitors, which then may be used to supply an electrical load. The sundoes not always shine on the solar cells with equal intensity however,and such systems are required to operate at power levels that may varydepending on weather conditions, temperature, time of day, shadows fromobstructions, and even momentary shadows, causing solar cell poweroutput to fluctuate. Similar problems with output variability areexperienced with other power sources such as wind, piezoelectric,regenerative braking, hydro power, wave power, and so forth. It iscommon for energy harvesting systems to be designed to operate under thetheoretical assumption that the energy source is capable of deliveringat its maximum output level more-or-less all of the time. Thistheoretical assumption is rarely matched in practice. Ordinarily,systems are design to be robust enough for anticipated peak loads, butthis is done at the expense of efficiency during operation at lowerintensity levels.

Switch mode power supplies (SMPS) are commonly used in efforts toefficiently harvest intermittent and/or variable energy source outputpower for delivery to storage element(s) and/or load(s). The efficiencyof the SMPS generally is fairly high, so much so that the power outputof the SMPS is often almost equal to the power input to the SMPS.Careful planning and device characterization are often used to attemptto design a system capable of harvesting at the theoretical maximumpower level. In a PV system, for example, the maximum power output of asolar cell peaks at a load point specific to the particular solar cell.This maximum power output point varies across different individual solarcells, solar cell arrays, systems in which the solar cells are used, andwith the operating environment of system and solar cell. The maximumenergy harvesting capability of the electronic system therefore dependson the solar cell characteristics and the characteristics of the loadapplied to the solar cell. One example of a typical application is anelectronic system to harvest energy from a solar cell array in order tocharge a battery. Battery charging systems commonly have multiple modes,which include fast charging, charging at full capacity (also called 1Ccharging), and trickle charging. A typical SMPS regulates output voltageand operates under the theoretical assumption that the power input iscapable of delivering the maximum load requirements of the output. Inpractice, the output impedance of a PV cell is high, so as duty cyclechanges, input voltage also changes, which changes the output power ofthe PV cell. Thus, there is a problem with efficiently exploiting theenergy harvesting potential of PV systems and other low and/or variableintensity power sources.

In carrying out the principles of the present invention, in accordancewith preferred embodiments, the invention provides advances in the artswith novel apparatus directed to harvesting energy under conditions ofboth low and high input power. In preferred embodiments, the apparatusincludes systems and circuits configured to operate at low power levelsand at power levels several orders of magnitude higher. Such systems aredesigned for harvesting and preferably storing energy available in anoperating environment in which power input may vary by several orders ofmagnitude.

According to aspects of the invention, examples of preferred embodimentsinclude systems for harvesting energy from variable output energyharvesting apparatus suitable for providing energy input to a switchedmode power supply. A control loop includes logic for dynamicallyadjusting energy harvesting apparatus power input to the switched modepower supply, ultimately regulating the system output power signalproduced by the switched mode power supply.

According to aspects of the invention, examples of the preferredembodiments include systems for harvesting energy using solar cells.

According to aspects of the invention, examples of preferred embodimentsof systems for harvesting energy from variable sources include a boostconfiguration.

According to aspects of the invention, examples of preferred embodimentsof systems for harvesting energy from variable sources include a buckconfiguration.

According to aspects of the invention, examples of preferred embodimentsof systems for harvesting energy from variable sources include abuck-boost configuration.

The invention has advantages including but not limited to one or moreof, improved energy harvesting efficiency, improved operating ranges forcharging systems, and reduced costs. These and other potentialadvantageous, features, and benefits of the present invention can beunderstood by one skilled in the arts upon careful consideration of thedetailed description of representative embodiments of the invention inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from considerationof the following detailed description and drawings in which:

FIG. 1 is a simplified schematic drawing illustrating an example of apreferred embodiment of a variable power energy harvesting system in afixed voltage boost configuration;

FIG. 2 is a simplified schematic drawing illustrating an example of apreferred embodiment of a variable power energy harvesting system in atemperature sensitive boost configuration;

FIG. 3 is a simplified schematic drawing providing an alternative viewof an example of a preferred embodiment of a variable power energyharvesting system in a boost configuration;

FIG. 4 is a process flow diagram illustrating an example of theoperation of a preferred embodiment of a variable power energyharvesting system;

FIG. 5 is a simplified schematic drawing illustrating an example of apreferred embodiment of a variable power energy harvesting system in abuck configuration;

FIG. 6 is a simplified schematic drawing providing an alternative viewof an example of a preferred embodiment of a variable power energyharvesting system in a buck configuration;

FIG. 7 is a simplified schematic drawing illustrating an example of apreferred embodiment of a variable power energy harvesting system in aboost-buck configuration;

FIG. 8 is a simplified schematic drawing illustrating an example of apreferred embodiment of a variable power energy harvesting system in abuck configuration having a parallel charge pump; and

FIG. 9 is a simplified schematic drawing illustrating an example of apreferred embodiment of a variable power energy harvesting system havinga configurable stack of energy harvesting apparatus and integratedstorage capacitors.

References in the detailed description correspond to like references inthe various drawings unless otherwise noted. Descriptive and directionalterms used in the written description such as right, left, back, top,bottom, upper, side, et cetera, refer to the drawings themselves as laidout on the paper and not to physical limitations of the invention unlessspecifically noted. The drawings are not to scale, and some features ofembodiments shown and discussed are simplified or amplified forillustrating principles and features as well as advantages of theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The variable power energy harvesting system of the invention may beembodied in several alternative configurations for efficientlyharvesting energy during alternatively low and high power inputconditions, such as a solar system for example, which may operate underboth low and high insolation conditions wherein available input powermay vary by orders of magnitude. In a solar powered system, for example,under low insolation conditions, such as cloudy outdoor, conditions orindoors, solar panel power output is greatly reduced. It is oftennevertheless desirable to harvest the small amount of available energy.The harvested energy may be used to run a low-power system or may bestored in batteries or other storage elements. In low power batteryoperated systems, this harvested energy can be enough to eliminate drainfrom standby power, extending battery life. This can facilitatecontinual operation without the frequent need for additional externalcharging. It is also often desirable to have the capability to maximizeenergy harvesting under high insolation conditions with the same system.This can require multiple modes of operation to get the most power froma solar panel, when the available power can change by several orders ofmagnitude, such as when moving a portable solar powered system fromwithin a building having artificial lighting out into direct sunlight.Due to these and other challenges and potential problems with thecurrent state of the art, improved methods, apparatus, and systems forenergy harvesting would be useful and advantageous.

Initially referring primarily to FIG. 1, an exemplary embodiment of avariable power energy harvesting system 100 has a control loop 102,which includes control logic 104. The system uses comparators 106 toassess the available harvested voltage, e.g., V_(PANEL) in relation topreselected high and low levels. A boost converter 110 with thelow-power hysteretic control loop 102 based on harvested voltageV_(PANEL) is used to regulate the power harvesting apparatus, in thisexample solar panel array 112, at its MPPT (Maximum Power PointTracking) voltage. The hysteretic control loop 102 may be run as theonly control, or may be used in conjunction with additional control(s)when the available harvested power is sufficient to power additionalcontrol circuitry.

For example, the system may include the capability to detect thecondition that power is being delivered to a load above a thresholdlevel, and then engage a more sophisticated MPPT regulation control. Thepower required for the operation of the MPPT regulation is preferablysmall relative to the available harvested power. Optionally, atemperature sensor may be provided for monitoring operating temperature.Operating temperature may be used to adjust the harvested voltage basedon temperature-induced effects on system performance. Now referringprimarily to FIG. 2, an example of an embodiment of such a variablepower energy harvesting system 200 is shown. It has been found thatactively monitoring output power V_(BATT) enables the system to choosethe optimum harvested voltage V_(PANEL) to maximize power output, e.g.,V_(BATT), realized from the solar panel array 112. A suitable currentsensor 202 is used to track the output V_(BATT). In the event theharvested voltage V_(PANEL) is less than output voltage V_(BATT), asdetermined by the sensor 202, the control logic 104 may be used toselect the optimal output voltage level V_(BATT) with a view towardmaximizing power harvested V_(PANEL)) from the solar panel 112. Thecurrent sensor 202 and MPPT (digital to analog converter) DAC 204provide the functionality needed by the control loop 102 to improve theenergy harvesting efficiency of the system 200 based on the conditionsexperienced by the energy source, e.g. solar panel 112, that affect thevoltage available (e.g., V_(PANEL)) for use by the system 200. In thecase of low-power applications for which it is particularly desirable tomonitor the load, such as portable electronics powered by a battery, thesystem 200 may be configured to briefly wake up to check the status ofthe load, e.g., V_(BATT), and determine whether conditions allow thesystem to continue charging. This wake up is preferably operated at arelatively low duty cycle, so as to not dramatically change the powerdelivered to the load V_(BATT).

Alternative views of an exemplary embodiment of a variable power energyharvesting system are shown in FIG. 3, depicting a schematic diagram ofthe system 300, and FIG. 4, illustrating the operation of the system300. In this example, a DC/DC synchronous switching Li-ion BatteryCharger system 300 includes fully integrated power switches, internalcompensation 302, and full fault protection 304. The system 300 utilizestemperature-independent photovoltaic Maximum Power Point Tracking (MPPT)circuitry 306 to provide power output V_(BATT) from energy harvestingapparatus 312 during Full Charge Constant-Current (CC) mode. A preferredswitching frequency of 1 MHz enables the use of small filter components,resulting in system size and cost advantages. In a presently preferredembodiment, in Full-Charge mode the duty cycle is controlled by the MPPTregulator 306. Once termination voltage is reached, the regulatoroperates in voltage mode. When the regulator is disabled (EN is low),the system draws less than 10 uA quiescent current.

Now referring primarily to FIG. 4, an example of the operation of thevariable power energy harvesting system in the context of a solarbattery charger is shown. When the output voltage, such as batterycharging voltage, is at a low threshold, e.g., below 3.0 volts in thisexample, the system 300 enters a pre-charge state and applies a small,programmable charge current to safely charge the battery to a level forwhich full charge current can be applied. Once the full charge mode hasbeen initiated, the system 300 attempts to maximize available chargecurrent to the battery by adjusting its duty cycle to regulate its inputvoltage to the MPP voltage of the energy harvesting apparatus, in thisexample photovoltaic cells. If sufficient current is available from thePV cell to exceed the safe 1C charge rate of the battery, then theprogrammable 1C current limit function will take priority over the MPPcontrol function and the PV cell voltage will rise above the MPP value.When the battery voltage has increased sufficiently to warrant enteringa maintenance mode (constant voltage), the PWM control loop forces aconstant voltage across the battery. Once in constant voltage mode,current is monitored to determine when the battery is fully charged.This regulation voltage as well as the 1C charging current may be set tochange based on battery temperature. For example, in a preferredembodiment, there are four temperature ranges which may be setindependently, for example, 0-10° C., 10-45° C., 45-50° C. and 50-60° C.The 0° C. and 60° C. thresholds stop charging and have 10 degrees ofhysteresis. The intermediate points have 1 degree of hysteresis. Athermal shutdown is also provided. In the event the temperature of thesystem exceeds 170° C. (in typical implementations), the SW outputstri-state in order to protect the system 300 from damage. The nFLT andall other protection circuitry remains active to inform the system 300of the failure mode. Once the system 300 cools sufficiently, e.g., to160° C. (typical), the system 300 attempts to restart. If the system 300reaches 170° C., the shutdown/restart sequence repeats. An internalcurrent limit is preferably maintained. The current through the inductoris sensed on a cycle by cycle basis and in the event a selected currentlimit is reached, the cycle is abbreviated. Current limit is alwaysactive when the regulator is enabled. An under-voltage lockout featureis also preferably provided. In this example, the system 300 is held inthe “off” state until the harvested voltage V_(PANEL) reaches a selectedthreshold, 3.6V, for example. There is preferably a 200 mV hysteresis onthis input, which requires the input to fall below 3.4V before thesystem 300 disables. A battery over-voltage protection circuit designedto shutdown the charging profile if the battery voltage is greater thanthe termination voltage is also preferably provided. The terminationvoltage may preferably be changed based on user programming, so theprotection threshold is set to 2% above the termination voltage.Shutting down the charging profile puts the system in a fault condition.

A variable power energy harvesting system 500 is depicted in FIG. 5. Inthis exemplary preferred embodiment, a buck converter configuration isshown. In this system 500, the design is configured to anticipate theoperational condition that the harvested voltage V_(PANEL) may begreater than the required output voltage V_(BATT). When the availableharvested power is too low to power any active control circuitry, thepass device (SW1) in the buck converter 510 switches to the “on” state.This does not allow MPPT to function, but can nevertheless provide thehighest output power because the system power overhead can be almostzero. As an alternative, this can also be done with a parallel switch tothe main pass device. Similar to boost mode, the device can briefly wakeup to check load status and available harvested power, e.g., V_(PANEL).Again, this should be at a low enough duty cycle to not dramaticallychange the power delivered to the load. A second mode of operation in abuck configuration is a low power hysteretic control based on theharvested voltage (V_(PANEL)). This requires some power overhead, so theavailable power should be sufficient to run the required circuitry.Similar to the hysteretic control in the boost mode, this can be to afixed voltage, a changing voltage based on temperature, or an activecontrol that monitors the output power to regulate the energy harvestingapparatus, e.g., panel 512, to its MPPT voltage. Finally, in the eventthe available power is sufficient, a more sophisticated control may beactivated to allow for better MPPT regulation. The efficiency gains frombetter MPPT regulation should be significant enough to overcome theadditional power overhead in running the additional control.

Alternative views of an exemplary embodiment of a variable power energyharvesting system having a buck converter are shown in FIG. 6. Inpreferred embodiments, a “power good” (PG) pin is used to indicate afault condition or inability to charge. The output is an open-draintype. When EN is low, the system 500 is nominally active. Assuming nofault conditions, the PG pin is open. An external resistor R connectedbetween the PG pin and an external I/O rail pulls the PG output up tothe rail voltage, indicating that charging is underway. In the event afault occurs, the PG pin is pulled to ground. The three events which cantrigger a PG fault indication are preferably, input under-voltage,output over-voltage, and thermal shutdown.

In preferred embodiments, the boost configuration of the system 500 is aDC/DC synchronous switching boost converter with fully integrated powerswitches, internal compensation, and full fault protection. Atemperature-independent photovoltaic Maximum Power Point Tracking (MPPT)system 500 thus embodied endeavors to maximize output current to theload, making it advantageous as a supply for battery chargingapplications. A switching frequency of 2 MHz is preferably chosen toenable the use of small external components for portable applications.Examples of the operation of the system 500 are described for twotypical scenarios. In one example, an intermediate charger circuit maybe used between the system 500 and a battery or other storage element.The terminal voltage is set high. When the system starts up and rampsthe output voltage above the PG threshold, the PG flag is set. Until theload is capable of sinking the full amount of current available from theboost converter, the output rises to the light load regulation value of5.0V. Once sufficient load is applied to the system, the load itselfdetermines the output voltage of the converter. In this case, the MPPtracking function adjusts the harvested input voltage of the system inorder to maximize the output current (and thus output power) into theload. In another example, the system may be used to directly charge aLi-Ion Battery, with the terminal VTERM set low. Insolation of the PVpanel allows immediate charging of the battery. The MPP trackingfunction works to deliver the maximum possible charge current to thebattery until the termination voltage of 4.0V is reached. At this point,the device automatically transitions to an accurate voltage regulationmode to safely maintain a full charge on the battery. The currentthrough the inductor is sensed on a cycle by cycle basis and if currentlimit is reached, the cycle is abbreviated. Current limit is alwaysactive when the boost converter is enabled. If the temperature of thesystem exceeds a selected threshold, such as 150° C., for example, theSW outputs tri-state in order to protect the system from damage. The PGand all other protection circuitry remain active to inform the system ofthe failure mode. Once the system cools to a lower threshold, e.g., 140°C., the system attempts to restart. In the event the system againreaches 150° C., the shutdown/restart sequence repeats. The PG output ispulled low to signal the existence of a fault condition. The system 500preferably also has an output over-voltage protection circuit 504 whichprevents the system 500 from reaching a dangerously high voltage undersudden light load conditions. The typical over-voltage detectionthreshold is 102% of the terminal voltage value. In the event of such acondition, the PG output is pulled low to signal a fault condition.Input under-voltage protection 504 is also preferably provided. Thesystem 500 monitors its input voltage and does not permit switching tooccur when the input voltage drops below a selected threshold, e.g., 250mV. Switching resumes automatically once the input voltage is above ahigher selected threshold, e.g., 275 mV. In addition, the PG output ispulled low to signal a fault condition.

As shown in FIG. 7, the variable power energy harvesting system may beimplemented in a buck-boost configuration 600, that is, a configurationin which the harvested voltage V_(PANEL) may be greater or less than theload voltage V_(BATT). This can be done with all or part of the featuresof the boost and buck configurations shown and described herein workingin parallel with a control mechanism to select which function should beactive under given conditions. The buck-boost system 600 is a DC/DCsynchronous switching charge controller which utilizes atemperature-independent photovoltaic Maximum Power Point Tracking (MPPT)circuit in efforts to optimize power from energy harvesting apparatussuch as a solar panel. The system 600 controls FET devices in buck,boost, and buck/boost configurations in order to support a wide range ofsystem power levels and output voltages. A preferred 100 kHz switchingfrequency results in low system quiescent current levels. The system 600includes integrated battery charge controls for Li-Ion, NIMH and leadacid batteries. In Full-Charge mode the duty cycle is controlled by theMPPT regulator.

FIG. 8 illustrates an implementation of a variable power energyharvesting system 700 demonstrating a buck configuration similar to thatshown and described with reference to FIGS. 1-4, with the addition of aparallel charge pump to work when the harvested voltage V_(PANEL) isbelow the output V_(BATT). This charge pump is controlled to run whenthe harvested voltage V_(PANEL) is within a certain voltage range.

Any of the above configurations can be combined with a traditional MPPTcomponent. The system may be operated with the traditional MPPT solutionin a standby low power state while one of the above configurations isactive, and then begin to run when the available power is sufficient torun the traditional solution.

An additional alternative feature of a variable power energy harvestingsystem 800 is shown in FIG. 9. This embodiment illustrates aconfiguration in which, under ultra-low power conditions, the energyharvesting apparatus, such as an array of PV panels, can be reconfiguredto reduce losses. A PV panel is configured such that the cells may berecombined in series and/or parallel combinations in order to set theMPPT voltage of the panel to approximate the voltage of the load. Inthis case, the load may be connected directly to the panel output or asimple linear circuit may be used to connect the load. The reconfiguringof the stack may be controlled by polling the conditions or as part of acontrol loop to maximize energy harvesting.

Alternatively, or additionally, a single capacitor or array ofcapacitors may be connected to all or some portion(s) of the energyharvesting apparatus such as a solar panel stack. Once these capacitorsreceive a level of charge from the energy harvesting stack, e.g., solarcells, this charge may be combined together or transferred to the powercontrol circuitry for output. These capacitors are preferably controlledsuch that the voltage on the capacitors is held close to the MPP voltageof the energy harvesting apparatus. In the event of a low energyharvesting level, e.g., some of the solar panel is blocked so that it isnot producing sufficient power, the capacitors are used to providesubstitute power in the interim until a higher energy harvesting levelis achieved.

Many variations are possible within the scope of the invention. Inpreferred embodiments, the apparatus of the invention preferablyincludes circuitry adapted to provide the capability to regulate variouslevels of power produced by associated energy harvesting apparatus. Forpurposes of clarity, detailed descriptions of functions, components, andsystems familiar to those skilled in the applicable arts are notincluded. The methods and apparatus of the invention provide one or moreadvantages including but not limited to, improved energy harvestingefficiency and/or improved operating ranges for energy harvestingsystems. While the invention has been described with reference tocertain illustrative embodiments, those described herein are notintended to be construed in a limiting sense. For example, variations orcombinations of functions and/or materials in the embodiments shown anddescribed may be used in particular cases without departure from theinvention. Various modifications and combinations of the illustrativeembodiments as well as other advantages and embodiments of the inventionwill be apparent to persons skilled in the arts upon reference to thedrawings, description, and claims.

We claim:
 1. A single-chip system for harvesting energy from a variableoutput energy harvesting apparatus comprising: energy harvestingapparatus for providing energy input; a switched mode power supplyoperably coupled to receive the input of the energy harvestingapparatus, and for providing a system output power signal; and a controlloop having control logic for dynamically adjusting energy harvestingapparatus input to the switched mode power supply, thereby regulatingthe system output power signal, wherein the control loop furthercomprises a maximum power point tracking (MPPT) mode and a mode that isconfigured to exceed an MPPT mode voltage level.
 2. The system forharvesting energy according to claim 1 wherein the energy harvestingapparatus further comprises one or more photovoltaic cells coupled tothe single chip system.
 3. The system for harvesting energy according toclaim 1 wherein the switched mode power supply further comprises a boostconfiguration contained in the single chip system with battery thermalcontrol circuitry.
 4. The system for harvesting energy according toclaim 1 wherein the switched mode power supply further comprises a buckconfiguration contained in the single chip system with over and undervoltage protection circuitry.
 5. The system for harvesting energyaccording to claim 1 wherein the switched mode power supply furthercomprises a buck-boost configuration contained in the single chipsystem.
 6. The system for harvesting energy according to claim 1 whereinthe switched mode power supply is adapted to provide low power inputvoltage regulation contained in the single chip system.
 7. The systemfor harvesting energy according to claim 1 wherein the switched modepower supply is adapted to provide low power temperature independentMPPT regulation.
 8. The system for harvesting energy according to claim1 wherein the switched mode power supply is adapted to providehysteretic input voltage regulation.
 9. The system for harvesting energyaccording to claim 1 wherein the switched mode power supply is adaptedto provide a low power mode and polling capability contained in thesingle chip system.
 10. The system for harvesting energy according toclaim 1 wherein the switched mode power supply is adapted to provide alow power linear mode contained in the single chip system.
 11. Thesystem for harvesting energy according to claim 1 further comprising acharge pump in parallel with the switched mode power supply contained inthe single chip system.
 12. The system for harvesting energy accordingto claim 1 wherein the energy harvesting apparatus further comprises aplurality of energy harvesting devices in a reconfigurable stack coupledto the single chip system.
 13. The system for harvesting energyaccording to claim 1 further comprising one or more storage capacitorsinterposed between the energy harvesting apparatus single chip system.14. The system for harvesting energy according to claim 1 furthercomprising a load operably coupled to the single chip system forreceiving the system output power signal.
 15. A system comprising: anenergy harvesting apparatus configured to provide an energy input; asingle chip system comprising: a switched mode power supply operablycoupled to receive the input of the energy harvesting apparatus, andconfigured to provide a system output power signal; and a control loophaving control logic configured to dynamically adjust the energy inputto the switched mode power supply as a function of battery hysteresisusing a maximum power point tracking (MPPT) mode and a mode that isconfigured to exceed an MPPT mode voltage level.
 16. The systemaccording to claim 15 wherein the switched mode power supply is adaptedto provide low power temperature-independent MPPT regulation.
 17. Asystem comprising: an energy harvesting apparatus for providing energyinput; a single chip system comprising: a switched mode power supplyoperably coupled to receive the input of the energy harvestingapparatus, and configured to provide a system output power signal; and acontrol loop having control logic configured to dynamically adjust anenergy harvesting apparatus input to the switched mode power supply,wherein the control loop further comprises a maximum power pointtracking (MPPT) mode and a mode that is configured to exceed an MPPTmode voltage level.
 18. The system according to claim 17 wherein theswitched mode power supply is adapted to provide a low power mode andpolling capability.
 19. The system according to claim 17 wherein theswitched mode power supply is adapted to provide hysteretic inputvoltage regulation.
 20. The system according to claim 17 wherein theswitched mode power supply is adapted to provide a low power linearmode.